This invention relates to a lubricative resin composition, a slide bearing made from such a composition, and a developing device including such a bearing.
Compactness and lightness in weight are key elements required for office automation (OA) devices such as copiers, laser beam printers (LBP) and facsimiles, and magnetic recording devices such as video tape recorders (VTR), and other devices. Various measures are taken for slide bearings for supporting rotary shafts as important parts of these devices.
Slide bearings made of resin and thus less likely to change in sliding properties with temperature are used more often than ever before in compact and lightweight devices.
Known suitable materials for such slide bearings include a synthetic resin such as polyamide resin, polyphenylene sulfide resin or polyacetal resin in which is dispersed and retained a lubricating oil, and a synthetic resin such as an aromatic polyamide resin to which is added polytetrafluoroethylene or modified polyolefin resin.
An oil-containing resin composition disclosed in examined Japanese patent publication 46-5321 is a composition manufactured by stirring polyacetal or polyamide powder in excess lubricating oil at a high temperature, i.e. a temperature higher than the melting point of the resin used, cooling and then powdering the obtained synthetic resin, and remolding the powdered resin. During molding, lubricating oil tends to bleed out, thus causing difficulty in feeding the material by means of an extruder screw. Excess lubricant thus tends to bleed out onto the surface of the end product.
As lubricants to be mixed with the synthetic resin, those having functional groups which can physically or chemically adsorb to the surface of a metallic mating member, such as hydroxy groups or carboxy groups, have been preferred so that the resin composition will stably exhibit good lubricity even if only a thin oil film is formed (boundary lubrication).
In the oil lubricating field, especially in a field where only a thin film is formed (boundary lubrication), it is said that lubricity varies widely with the type of oil used. Lubricants having functional groups that can physically or chemically adsorb to a metallic material (oil or additives) are regarded as good boundary lubricants. Hydroxy groups and carboxy groups are known as typical adsorptive functional groups.
In examined Japanese patent publication 48-37572, an oil-containing resin composition is disclosed which is a plastics having a melting point higher than the molding temperature of a base plastics (resin as a main component) or having, at molding temperatures, a viscosity higher than the melt viscosity of the base plastics, and having a specific surface area of 0.01 m.sup.2 /g or over, and containing a saturated or unsaturated higher fatty acid or its salt or ester, an amide, a chlorine compound or a metallic soap.
Examined Japanese patent publication 48-37572 utilizes good compatibility of polyethylene with hydrocarbon oil to provide an oil-containing resin composition containing a large amount of lubricating oil in a base plastics such as polyamide. The kind of hydrocarbon oil used is not limited.
When this conventional oil-containing resin composition is used at normal or higher-than-normal temperatures, lubricating oil is dispersed and retained in the form of droplets in the matrix (resin). This makes it difficult to supply lubricating oil onto the metal surface at a stable speed over a long period of time because the speed with which lubricant is supplied onto the surface varies with the distribution density of the lubricating oil droplets and their size.
Also, if a sliding state continues for a long time, it becomes increasingly difficult to lubricate sliding surfaces with such a conventional oil-containing resin composition, thus increasing the possibility of seizure.
If lubrication is insufficient on the surface of slide bearings supporting both ends of sensitizing rollers as developing agent carriers or latent image retainers in developing devices of copiers and LBP's, the rotating speed of the sensitizing rollers tends to fluctuate due to fluctuation in the slide resistance. This can cause a problem fatal to copiers and printers, i.e. blurred images.
Furthermore, conventional oil-containing resin compositions are not smoothly fed by an extruder screw for molding. Thus, the molded articles tend to suffer mold deposit (delamination). Also, a large amount of oil tends to bleed out onto the surface.
An object of the invention of the present application is to provide a highly wear-resistant lubricative resin composition, and to make a slide bearing from such a composition so that the friction coefficient can be maintained stably at a low level even if its sliding surface is used for a long time.
For the moldability of the lubricative resin composition, its physical properties should be controlled such that the composition can be supplied to a screw at a stable speed, and be fed reliably by the screw with little mold deposite, and that the molded article will be least likely to suffer delamination. Another object is to prevent excessive bleeding of oil onto the surface of the molded article.